The official repository is at libntl.org , where you can find the latest Unix ( .tar.gz ) and Windows ( .zip ) distributions.
The .ntl file suffix is often related to scripts for the D2NT mod in Diablo 2. Where to Download Download NTL rar
For other NTL-related projects, reputable hosting sites like SourceForge are common. How to Open a .rar File The official repository is at libntl
A widely used C++ library for high-performance number theory, often used in cryptography and computer algebra. The official repository is at libntl.org